Fuel cells have been proposed as a power source for electric vehicles and other applications. In proton exchange membrane (PEM) type fuel cells, hydrogen is supplied to an anode of the fuel cell and oxygen is supplied as an oxidant to a cathode. A plurality of fuel cells are stacked together in fuel cell stacks to form a fuel cell system. Typically, numerous fuel cells are required to power fuel cell powered vehicles. Large amounts of hydrogen stored in a tank on the vehicle are supplied to each of the fuel cell stacks to power the fuel cell stacks. The fuel and oxidant are typically stored in large pressurized fuel tanks disposed on an undercarriage of the vehicle.
Typically, fuel tanks are cylindrical in shape, and are disposed transversely on the undercarriage of the vehicle, behind the rear passenger seats and between the rear wheels. Current fuel tanks are manufactured using a rotational molding method. A tank is formed utilizing the rotational molding method by: disposing bosses in a die cavity with a polymer resin, heating the mold while it is rotated causing the resin to melt and coat walls of the die cavity, cooling the die, and removing the molded tank. The rotational molding method may be used to produce nearly any hollow, one layer part including an inserted, integrated boss. However, the rotational molding method has a long cycle time, typically completing only one to two cycles an hour. Accordingly, the rotational molding method is better utilized for the creation of only a small number of tanks. Further, because the rotational molding method may only be used with a single polymer level, the rotational molding method does not permit the formation of multilayered tanks. A multilayered polymer tank is desired because the hydrogen permeability of a single layer tank may be one thousand times more permeable than some multilayered blow molded tanks.
It would be desirable to develop a method and apparatus for forming a blow molded vessel having a plurality of bosses and adapted to store a fluid, wherein a plurality of bosses are disposed in a mold and a material is extruded into the mold and blow molded, the material adhering to the bosses and taking the desired shape of the mold.